According to the National Park Service (NPS), over 300 million visitors collectively spent over a billion hours at U.S. national parks in 2015. Those numbers are expected to go up this year, given the marketing efforts around the NPS’s centennial anniversary. But even without the anniversary, foot traffic at U.S. parks has been trending upward: In recent years, the NPS has seen record attendance, which has resulted in long lines and packed campsites at some of its most popular parks.

Attendance numbers are often provided as a crude measure of how much people like and value America’s national parks. But that is only a rough proxy for determining the parks’ economic value—a number that could have implications for how the parks are managed and funded.

So a group of researchers recently looked into that question: How much is the NPS—the parks and the services it provides—worth to Americans?  "One of the things that the country's not very good at is how we value public assets, whether those public assets are highways, bridges, or clean air. Here we have this enormous public asset and we didn't know how to value it," says Linda Bilmes, a professor at the Harvard Kennedy School and one of the co-authors of the study.*

Bilmes, along with Michelle Haefele and John Loomis, a postdoctoral fellow and a professor at Colorado State University respectively, estimate that NPS parks and programs are together worth about $92 billion. They arrived at this figure by using methods similar to those that federal agencies use in analyzing proposed regulations. First, they sent a survey to about 4,000 U.S. households asking how much residents were willing to pay in additional federal income taxes in order to keep America’s national parks. An estimate was then made based on the answers of the 700 households that responded, and those who didn’t respond were ascribed a value of zero. The $92 billion number breaks down into $62 billion for National Park lands and $30 billion for NPS programs, which include recreational activities, efforts to protect landmarks, and educational programs.

“What our study shows, which has never been studied before, is that people who don't necessarily visit the parks still place a very high value on protecting these places and these programs," says Bilmes. Sure, people who use national parks for hiking or camping value them, but what this estimate suggests is that for those who don’t use the parks, it seems that just the idea of having national parks around is attractive enough to be worth tax dollars. Additionally, Bilmes noted that $92 billion is a conservative estimate, since those who didn’t answer the survey were given zero values and a post-survey audit found that most of those who didn’t respond didn’t have time to fill out the survey—so it’s likely not the case that the parks are worth nothing to them. Separately, the demographics of park attendance could hurt the NPS’s long-term valuation given that the majority of its visitors are older white Americans, even as the U.S. becomes increasingly diverse.

Several foundations, including the National Park Foundation, a nonprofit, funded the study independently of the NPS with the aim of contributing to the conversation around how the NPS is funded. Bilmes was part of the National Parks Second Century Commission, which recommended a hybrid funding model—similar to the model at universities or the Smithsonian Institution—that would include an endowment to supplement annual appropriations for the NPS. Since the passing of government budgets is a highly politicized event, an endowment model would likely help with any instability that results from partisan squabbling.

Currently, the Obama administration is requesting a budget of $3.1 billion for the NPS for 2017—an amount that includes a bump for restoration and upgrades. It’s the hope of the study’s researchers that the government might start spending a bit more, or considering alternative funding models, in order to maintain a well-loved public asset.

* This article originally misspelled Linda Bilmes's last name as Blimes, and misstated the number of hours visitors spent at U.S. national parks. We regret the error.